Double-walled exhaust manifold

ABSTRACT

The invention relates to a double-walled exhaust manifold ( 10 ) for a motor vehicle, said exhaust manifold comprising at least one inner element ( 12 ) provided with sliding tubes ( 16, 18 ) which fit into each other, and an outer element ( 14 ) which is moulded from a single piece around the inner element ( 12 ) with which it determines an inner insulation cavity ( 20 ). The inventive exhaust manifold is characterised in that the inner element comprises at least one first straight upstream tube ( 22 ), a first end ( 24 ) of said tube being arranged in the extension of an exhaust line of an associated heat engine cylinder head and a second end ( 26 ) fitting together, in a sliding manners with an intermediate part ( 28 ) of at least one downstream tube ( 16, 18 ) having an axis (B) intersecting the axis (A) of the first tube ( 22 ).

The invention relates to a double-walled exhaust manifold for a motor vehicle.

The invention relates more particularly to a double-walled exhaust manifold for a motor vehicle, of the type provided with at least one internal manifold element and one external manifold element, of the type in which the internal manifold element is provided with at least two coaxial tubes nested slidingly one inside the other, and of the type in which the external manifold element is cast in one piece around the internal manifold element, with which it defines an internal insulating cavity disposed between the internal manifold element and the external manifold element.

Numerous examples of exhaust manifolds of this type are known.

U.S. Pat. No. 4,182,122 describes and illustrates a manifold of the type described in the foregoing, wherein the internal manifold element is provided with at least one internal tube of “T” shape, whose central branch is connected to an exhaust conduit of the cylinder head and whose symmetric branches, with their axis intersecting the axis of the central branch, are each connected slidingly to at least one other internal tube.

The internal connector element is separated from the external manifold element by a “T” shaped insulator made in two pats and mounted with clearance between the internal manifold element and the external manifold element.

This design poses numerous problems of resistance to heat.

On the one hand, the insulator actually ensures that the external manifold element will not be exposed to excessively high temperatures. To the contrary, it concentrates the heat resulting from the rise in temperature of the internal manifold element around that element.

On the other hand, the “T” shape of the aforesaid internal tube subjects it to elevated mechanical constraints when it expands as a result of the rise in temperature of the internal manifold element. This expansion, which is not compensated between the central branch and the symmetric branches of the internal “T” tube, may result in rupture thereof.

The invention remedies these drawbacks by proposing a manifold in which, on the one hand, the external manifold element is insulated from the internal manifold element and, on the other hand, in which all the internal tubes of the internal manifold element are tubes of substantially long shape mounted slidingly one inside the other in such a way as to absorb the deformations resulting from the rise in temperature of the manifold during use thereof.

With this objective, the invention proposes a manifold of the type described hereinabove, characterized in that the internal manifold element is provided with at least one straight first upstream tube, a first end of which is disposed in the extension of an exhaust conduit of a cylinder head of an associated heat engine, and a second end of which is nested slidingly with an intermediate part of at least one downstream tube whose axis intersects the axis of the said first upstream tube, thus permitting expansion of the said internal manifold element during the rise in temperature of the manifold.

According to other characteristics of the invention:

-   -   the exhaust manifold is provided with at least one elbowed         second upstream tube, a first end of which is disposed in the         extension of an exhaust conduit of the cylinder head and a         second end of which, with axis intersecting that of the first         end, is nested slidingly with the end of a downstream tube,     -   the exhaust manifold is provided with at least two downstream         tubes, one end of one downstream tube being nested slidingly         with the end of the other downstream tube,     -   the external manifold element is cast in such a way that it         confines at least a first end of an upstream tube and an end of         a downstream tube,     -   the external manifold element is provided with a bore that         communicates with the internal insulating cavity to permit         evacuation of a sand core used to form the insulating cavity         during casting of the said external manifold element,     -   the tubes of the internal manifold element are made of steel.

The invention also proposes a method for manufacturing an exhaust manifold of the type described hereinabove, characterized in that it includes at least:

-   -   a first step of manufacture of tubes of the internal manifold         element,     -   a second step of assembly of the tubes of the internal manifold         element with one another,     -   a third step, in the course of which the tubes of the internal         manifold element are placed in a machine making it possible to         form, around the tubes, a sand core intended to permit casting         of the insulating cavity,     -   a fourth step of casting of the said sand core,     -   a fifth step, in the course of which the tubes of the internal         manifold element and the sand core are placed in a mold         containing an imprint of the external manifold element,     -   a sixth step of casting of the external manifold element,     -   a seventh step of removal of the external manifold element from         the mold,     -   an eighth step of removal of the sand core by abrasive blasting,     -   a ninth step of machining of the manifold,     -   and a tenth step of mounting of a sealing plug in the bore of         the external manifold element.

Other characteristics and advantages of the invention will become apparent from reading the detailed description hereinafter which will be understood by referring to the attached drawings wherein:

FIG. 1 is a schematic view in longitudinal section of a manifold according to the invention;

FIG. 2 is a schematic view in transverse section of the manifold of FIG. 1;

FIG. 3 is a schematic view in longitudinal section of a manifold according to an alternative embodiment;

FIG. 4 is a schematic view in transverse section of the manifold of FIG. 3.

In the description hereinafter like reference numerals denote like parts or parts having similar functions.

The figures illustrate the entirety of a double-walled exhaust manifold 10 for a motor vehicle.

As illustrated in FIG. 1, manifold 10 is provided with at least one internal manifold element 12 and one external manifold element 14. External manifold element 14 is provided with a first flange 13 intended to be fixed to the cylinder head (not illustrated) of an associated engine, and with a second flange 15 intended to be fixed to an exhaust pipe (not illustrated) of the vehicle.

In known manner, internal manifold element 12 is provided with at least two coaxial tubes 16, 13 nested slidingly one inside the other in order to permit a certain expansion of internal manifold element 12 when it is subjected to a temperature rise.

Moreover, external manifold element 14 is cast in known manner in one piece around internal manifold element 12, with which it defines an internal insulating cavity 20 disposed between internal manifold element 12 and external manifold element 14. By virtue of a phenomenon known as “air layer”, this cavity 20 makes it possible to insulate external manifold element 14 from the heat released by internal manifold element 12 during the rise in temperature of manifold 10, without interposing any insulation whatsoever between the two manifold elements 12, 14 and thus risking concentrating the heat on internal manifold element 12.

According to the invention, as illustrated in FIG. 1, internal manifold element 12 is provided with at least one straight first upstream tube 22, a first end 24 of which is disposed in the extension of an exhaust conduit (not illustrated) of a cylinder head of an associated heat engine, and a second end 26 of which is nested slidingly with an intermediate part 28 of at east one downstream tube 16, 18, whose axis “B” intersects axis “A” of the said upstream tube 22, thus permitting expansion of the said internal manifold element 12 during the rise in temperature of manifold 10.

Furthermore, exhaust manifold 10 is provided with at least one elbowed second upstream tube 30, a first end 32 of which is disposed in the extension of an exhaust conduit (not illustrated) of the cylinder head, and a second end 34 of which, whose axis “B” intersects axis “A” of the first end, is nested slidingly with end 36 of a downstream tube 18.

In the preferred embodiment of the invention, but without being limited thereto, exhaust manifold 10 is provided with at least two downstream tubes 16, 18, one end 38 of one downstream tube 16 being nested slidingly with end 40 of the other downstream tube 18.

More particularly, in the example illustrated in FIG. 1, according to which manifold 10 is adapted to a cylinder head of a three-cylinder engine provided with three exhaust conduits, manifold 10 is provided with two straight first upstream tubes 22, an elbowed second upstream tube 30, and two downstream tubes 16, 18, the intermediate parts 28 of which receive the first two upstream tubes 22. One end 42 of downstream tube 16 communicates with an outlet orifice 44 of manifold 10.

This configuration is obviously not limitative of the invention, and such a manifold 10 can easily be adapted to a cylinder head provided with a larger or smaller number of exhaust conduits.

According to the invention, external manifold element 14 is cast in such a way that it confines at least one first end 24, 32 of an upstream tube 22, 30 and one end 42 of a downstream tube 16. This configuration, established during casting of external manifold element 14, allows internal manifold element 12 to be joined simply and effectively to external manifold element 14. It is then external manifold element 14 that is connected respectively to the cylinder head of the associated engine and to the rest of the exhaust system of the vehicle, Tubes 16, 18, 22, 30 of the internal manifold element are made of steel to facilitate confinement of their ends by external manifold element 14.

Furthermore, external manifold element 14 is provided with a bore 46, which communicates with internal insulating cavity 20 to permit evacuation of a sand core used to form insulating cavity 20 during casting of the said external manifold element 14.

In this configuration, exhaust manifold 10 can be produced very simply according to a method that includes at least:

-   -   a first step of manufacture of tubes 16, 18, 22, 30 of internal         manifold element 12.     -   a second step of assembly of tubes 16, 18, 22, 30 of internal         manifold element 12 with one another,     -   a third step, in the course of which tubes 16, 13, 22, 30 of         internal manifold element 12 are placed in a machine (not         illustrated) making it possible to form around the tubes, a sand         core (not illustrated) intended to permit casting of insulating         cavity 20,     -   a fourth step of casting of the said sand core,     -   a fifth step, in the course of which tubes 16, 18, 22, 30 of         internal manifold element 12 and the sand core are placed in a         mold (not illustrated, containing an imprint of external         manifold element 14,     -   a sixth step of casting of external manifold element 14,     -   a seventh step of removal of external manifold element 14 from         the mold,     -   an eighth step of removal of the sand core by abrasive blasting,     -   a ninth step of machining of manifold 10,     -   and a tenth step of mounting of a sealing plug in bore 46 of the         external manifold element 14.

The invention therefore makes it possible in simple and effective manner, to make a “double-walled” exhaust manifold 10 in which the expansion of tubes 16, 18, 22, 30 of internal element 12 is absorbed by mechanical clearances in all directions, in such a way that it does not affect the strength of the said manifold 10.

According to alternative embodiment illustrated in FIGS. 3 and 4, the end (24) of the straight first upstream tube (22) and the first end (32) of the elbowed second upstream tube (30) can extend to the first face (13) of the external manifold element (14). Similarly, the end (42) of the downstream tube (16) can extend to the second face (15) of the external manifold element (14).

This alternative makes it possible to avoid confining at least one first end 24, 32 of an upstream tube 22, 30 and one end 42 of a downstream tube 16, as was described hereinabove with reference to FIGS. 1 and 2.

Ends 24 and 32, which extend to first face 13 of external element 14, can be in contact with the ends of the exhaust conduits of the cylinder head. Similarly, end 42, which extends to second face 15 of external element 14, can be in contact with one end of the exhaust pipe of the engine. This configuration ensures leaktightness relative to the exhaust gas of the engine. Thus external element 14 is not in direct contact with the exhaust gases, there are no risks of corrosion. To achieve this configuration tubes 22, 30 and 16 are positioned, relative to the mold used to make external element 14, in such a way that they protrude beyond this external element 14 once this casting operation has been completed. It is necessary, however, to provide an operation of machining of these tubes, to eliminate the protruding segments. This operation can be performed at the same the operation of machining of manifold 10.

Manifold 10 can be provided with means for preventing axial displacement of the ends 24, 32 and 42 of upstream tubes 22, 30 and downstream tube 16 that extend to faces 13 and 15 of external element 14. Examples of such means are annular grooves or shoulders made on upstream tubes 22, 30 and downstream tube 16 at the position of the segments in contact with external element 14, in such a way that, during casting of external element 14, the molten material defines a shape complementary to those means in order to prevent axial displacement. Consequently, ends 24, 32 and 42 will be fixed relative to external element 14, and will always be able to ensure contact with the ends of the exhaust conduits of the cylinder head and of the exhaust pipe. 

1-13. (canceled)
 14. A double-walled exhaust manifold for a motor vehicle, comprising: at least one internal manifold element and one external manifold element, wherein the internal manifold element includes at least two coaxial tubes nested slidingly one inside the other, and the external manifold element is cast in one piece around the internal manifold element, with which the external manifold element defines an internal insulating cavity disposed between the internal manifold element and the external manifold element, and wherein the internal manifold element includes at least one straight first upstream tube, a first end of which is disposed in an extension of an exhaust conduit of a cylinder head of an associated heat engine, and a second end of which is nested slidingly with an intermediate part of at least one downstream tube whose axis intersects the axis of the first upstream tube, thereby permitting expansion of the internal manifold element during a rise in temperature of the manifold.
 15. An exhaust manifold according to claim 14, comprising at least one elbowed second upstream tube, a first end of which is disposed in an extension of an exhaust conduit of the cylinder head and a second end of which, with its axis intersecting the axis of the first end, is nested slidingly with the end of a downstream tube.
 16. An exhaust manifold according to claim 14, comprising at least two downstream tubes, one end of one downstream tube being nested slidingly with the end of the other downstream tube.
 17. An exhaust manifold according to claim 14, wherein the external manifold element includes a bore that communicates with the internal insulating cavity to permit evacuation of a sand core used to form the insulating cavity during casting of the external manifold element.
 18. An exhaust manifold according to claim 14, wherein the tubes of the internal manifold element are made of steel.
 19. An exhaust manifold according to claim 14, wherein the external manifold element is cast to confine at least one first end of an upstream tube and one end of a downstream tube.
 20. An exhaust manifold according to claim 15 wherein the end of the straight first upstream tube and the first end of the elbowed second upstream tube extend to the first face of the external manifold element.
 21. An exhaust manifold according to claim 20, wherein one end of a downstream tube extends to a second face of the external manifold element.
 22. An exhaust manifold according to claim 21, further comprising means for preventing axial displacement of the ends of the upstream tubes and downstream tube that extend to the faces of the external manifold element.
 23. A method for manufacturing an exhaust manifold according to claim 14, comprising: a first step of manufacture of the tubes of the internal manifold element, a second step of assembly of the tubes of the internal manifold element with one another, a third step, during which the tubes of the internal manifold element are placed in a machine making it possible to form around the tubes, a sand core intended to permit casting of the insulating cavity, a fourth step of casting of the sand core, a fifth step, during which the tubes of the internal manifold element and the sand core are placed in a mold containing an imprint of the external manifold element, a sixth step of casting of the external manifold element, a seventh step of removal of the external manifold element from the mold, an eighth step of removal of the sand core by abrasive blasting, a ninth step of machining of the manifold, and a tenth step of mounting of a sealing plug in the bore of the external manifold element.
 24. A method for manufacturing an exhaust manifold according to claim 14, comprising: a first step of manufacture of the tubes of the internal manifold element, a second step of assembly of the tubes of the internal manifold element with one another, a third step, during which the tubes of the internal manifold element are placed in a machine making it possible to form, around the tubes, a sand core intended to permit casting of the insulating cavity, a fourth step of casting of the said sand core, a fifth step, during which the tubes of the internal manifold element and the sand core are placed in a mold containing an imprint of the external manifold element, a sixth step of casting of the external manifold element, a seventh step of removal of the external manifold element from the mold, an eighth step of removal of the sand core by abrasive blasting, a ninth step of machining of the manifold and of the ends of the tubes that protrude beyond the faces of the external element, and a tenth step of mounting of a sealing plug in the bore of the external manifold element.
 25. An internal combustion engine provided with a cylinder head and an exhaust manifold according to claim 20, wherein the ends which extend to the first face of the external element are in contact with the ends of the exhaust conduits of the cylinder head.
 26. An internal combustion engine according to claim 25, wherein the end which extends to the second face of the external element is in contact with one end of the exhaust pipe of the engine. 